1. Field of the Invention
The present invention relates to a piezoelectric ceramic mainly comprised for example of a PZT (zirconia-lead titanate)-based material or PT (lead titanate)-based material and a piezoelectric device using the same, more particularly relates to a piezoelectric ceramic superior in mechanical strength while maintaining its piezoelectric characteristics and easy to produce inexpensively and a piezoelectric device using the same.
2. Description of the Related Art
This type of piezoelectric ceramic is widely used for piezoelectric resonators, ceramic filters, piezoelectric elements, piezoelectric buzzers, piezoelectric transformers, ultrasonic vibrators, and other piezoelectric devices.
Among these, high frequency ceramic resonators and other high frequency piezoelectric devices use the above PZT-based materials and PT-based materials and, further, ceramic materials consisting of these plus second ingredients or third ingredients substituted with these and additives added (for example, see Japanese Unexamined Patent Publication (Kokai) No. 5-58724).
In a device like a piezoelectric device driven by a large amplitude, impact, of course, and also a rise in the input voltage causing oscillation at a large amplitude are liable to sometimes cause destruction at a stress concentration point called a xe2x80x9cnode pointxe2x80x9d, so a piezoelectric ceramic device is considered required to have a sufficiently large mechanical strength while maintaining its piezoelectric characteristics when made particularly thin.
For example, Japanese Unexamined Patent Publication (Kokai) No. 6-112542 proposed to make the particle size of the powder material small to reduce the surface ratio to less than 10 m2/g and to provisionally sinter it at a temperature of less than 650xc2x0 C. to reduce the crystalline size of the device to less than 1 xcexcm since there is a large correlation between voids and other crystal defects and mechanical strength in a piezoelectric ceramic. Further, it proposed to enhance the mechanical strength by the hot press method.
Further, to improve one of the piezoelectric characteristics, the electromechanical coupling factor kt, for example, Japanese Examined Patent Publication (Kokoku) No. 59-41311 proposes to replace part of the lead oxide in a composition mainly comprised of lead titanate with samarium oxide.
In this method of improving the mechanical strength by making the powder material finer in size, however, a separate step is required for making the powder finer in size. Further, the fine powder material is extremely difficult to handle in the manufacture of a piezoelectric ceramic device.
Further, in the method of increasing the mechanical strength by the hot press method, the manufacturing time becomes longer and, further, expensive equipment is required, so there is a large cost demerit.
On the other hand, in the method of increasing the electromechanical coupling factor kt by replacing part of the lead oxide by samarium oxide, there were the problems that the composition become off and the piezoelectric characteristics deteriorated or that the costs became higher since a relatively inexpensive oxide was required.
An object of the present invention is to provide a piezoelectric ceramic superior in mechanical strength while maintaining its piezoelectric characteristics and easy to produce inexpensively and a piezoelectric device using the same.
To achieve this object, according to a first aspect of the present invention, there is provided a piezoelectric ceramic having a carbon content after sintering of less than 37 ppm by weight.
According to a second aspect of the present invention, there is provided a piezoelectric ceramic mainly comprised of lead zirconate titanate and having a carbon content after sintering of less than 36 ppm by weight. The lead zirconate titanate in this case is preferably
(Pb1xe2x88x92xMx)n{A1yA2(1xe2x88x92y)}aTibZrcO3
where,
0 less than x less than 0.1
2/6 less than y less than 5/6
0.0 1xe2x89xa6axe2x89xa60.2
0.2xe2x89xa6bxe2x89xa60.6
a+b+c=1
0.9xe2x89xa6nxe2x89xa61.1
M: one or more of Ca, Ba, and Sr
A1: one or more of Nb, Sb, Ta, W, and V
A2: one or more of Mg, Mn, Fe, Co, Ni, Zn, Sn, Cu, Cr, Sr, Y, Bi, and Ln (Ln: lanthanoid element).
Further, the first and second aspects of the invention more preferably have carbon contents after sintering of over 3 ppm by weight.
Further, according to a third aspect of the present invention, there is provided a piezoelectric ceramic mainly comprised of lead titanate and having a carbon content after sintering of less than 37 ppm by weight. The lead titanate in this case is preferably
(Pb1xe2x88x92axe2x88x92bMaBib)n(Ti1xe2x88x92xxe2x88x92yMnxNby)O3
where,
0 less than x less than 0.1
0.01xe2x89xa6axe2x89xa60.5
0.01xe2x89xa6bxe2x89xa60.30
0.005xe2x89xa6xxe2x89xa60.05
0.005xe2x89xa6yxe2x89xa60.05
0.9xe2x89xa6nxe2x89xa61.1
M: one or more of Ca, Ba, Sr, and Ln (Lan: lanthanoid element).
In the third aspect of the invention, the carbon content after sintering is more preferably over 4 ppm by weight.
The present inventors further took note of the carbon content of the piezoelectric after sintering and discovered that the mechanical strength could be sufficiently raised by making it less than 37 ppm by weight (less than 36 ppm by weight for the second aspect of the invention and less than 37 ppm by weight for the third aspect of the invention). Further, to maintain the piezoelectric characteristics, in the first and second aspects of the present invention, the carbon content is preferably over 3 ppm by weight (over 4 ppm by weight in the third aspect of the present invention).
A more preferable range of carbon content is 7 ppm by weight to 29 ppm by weight (8 ppm by weight to 29 ppm by weight for the third aspect of the invention).
If the carbon content after sintering is 3 ppm by weight (4 ppm by weight for the third aspect of the invention), the electromechanical coupling factor kt and other piezoelectric characteristics fall and the transmittance band of the signal when used for a piezoelectric ceramic filter is limited, but this is not a practical problem.
Conversely, if the carbon content after sintering is 37 ppm by weight (36 ppm by weight for the second aspect of the invention and 37 ppm by weight for the third aspect of the invention), it is not possible to obtain a sufficiently sintered material body.
Note that the carbon content after sintering is mainly due to the carbonates of the material of the piezoelectric and the carbon component in the organic binder.
The piezoelectric ceramics according to the first to third aspects of the invention may be used as the piezoelectric of piezoelectric resonators, ceramic filters, piezoelectric elements,piezoelectric buzzers, piezoelectric transformers, ultrasonic vibrators, and other piezoelectric devices. Among these, the piezoelectric ceramic according to the second aspect of the present invention is preferably applied to a piezoelectric element or piezoelectric transformer or other drive device, while the piezoelectric ceramic according to the third aspect of the present invention is preferably applied to a resonator or filter etc.
According to the present invention, it is possible to provide a piezoelectric ceramic superior in mechanical strength while maintaining its piezoelectric characteristics and easy to produce inexpensively and a piezoelectric device using the same.
The present disclosure relates to subject matter contained in Japanese Utility Model Application No. HEI 11-188338,filed on Jul. 2, 1999, the disclosure of which is expressly incorporated herein by reference in its entirety.